U.S. patent application number 11/374044 was filed with the patent office on 2006-07-20 for process for reducing the production of water in oil wells.
This patent application is currently assigned to ENI S.p.A.. Invention is credited to Maria Andrei, Giovanni Burrafato, Luisa Chiappa, Thomas Paul Lockhart, Giuseppe Maddinelli.
Application Number | 20060157245 11/374044 |
Document ID | / |
Family ID | 11447759 |
Filed Date | 2006-07-20 |
United States Patent
Application |
20060157245 |
Kind Code |
A1 |
Chiappa; Luisa ; et
al. |
July 20, 2006 |
Process for reducing the production of water in oil wells
Abstract
A process is described for reducing the production of water in
oil wells which comprises the injection into the formation around
the well of an aqueous solution of one or more polymers selected
from those having general formula (1) [] wherein: n ranges from
0.70 to 0.98; m ranges from 0.30 to 0.02; n+m=1; X1 and X2, the
same or different, are selected from H an CH3; R1, R2, R3, the same
or different, are selected from C1-C10 monofunctional hydrocarbyl
groups; x ranges from 2 to 5.
Inventors: |
Chiappa; Luisa; (Nerviano
Milan, IT) ; Andrei; Maria; (Mediglia Milan, IT)
; Lockhart; Thomas Paul; (Lodi, IT) ; Burrafato;
Giovanni; (Tavazzano Lodi, IT) ; Maddinelli;
Giuseppe; (Milan, IT) |
Correspondence
Address: |
OBLON, SPIVAK, MCCLELLAND, MAIER & NEUSTADT, P.C.
1940 DUKE STREET
ALEXANDRIA
VA
22314
US
|
Assignee: |
ENI S.p.A.
Rome
IT
ENITECNOLOGIE S.p.A.
San Donato Milanese Milan
IT
|
Family ID: |
11447759 |
Appl. No.: |
11/374044 |
Filed: |
March 14, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10478321 |
Nov 20, 2003 |
|
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PCT/EP02/05325 |
May 10, 2002 |
|
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11374044 |
Mar 14, 2006 |
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Current U.S.
Class: |
166/295 ;
166/294; 507/223 |
Current CPC
Class: |
C09K 8/5083 20130101;
C09K 8/5753 20130101 |
Class at
Publication: |
166/295 ;
166/294; 507/223 |
International
Class: |
E21B 33/138 20060101
E21B033/138 |
Foreign Application Data
Date |
Code |
Application Number |
May 25, 2001 |
IT |
MI2001A 001112 |
Claims
1. A process for reducing the production of water in oil wells
which comprises the injection into the formation around the well of
an aqueous solution of one or more polymers selected from those
having general formula (I) ##STR4## wherein: n ranges from 0.70 to
0.98; m ranges from 0.30 to 0.02; n+m=1; X.sub.1 and X.sub.2, the
same or different, are selected from H and CH.sub.3; R.sub.1,
R.sub.2, R.sub.3, the same or different, are selected from
C.sub.1-C.sub.10 monofunctional hydrocarbyl groups; x ranges from 2
to 5.
2. The process according to claim 1, characterized in that n ranges
from 0.80 to 0.95 and m ranges from 0.20 to 0.05.
3. The process according to claim 1, characterized in that R.sub.1,
R.sub.2, R.sub.3, the same or different, are selected from
C.sub.1-C.sub.3 monofunctional alkyl radicals.
4. The process according to claim 3, characterized in that
R.sub.1.dbd.R.sub.2.dbd.R.sub.3.dbd.CH.sub.3.
5. The process according to claim 1, characterized in that x=3.
6. The process according to claim 1, characterized in that the
polymer having general formula (I) has a molecular weight ranging
from 1.5 to 12 million.
7. The process according to claim 1, characterized in that the
concentration of the polymer having general formula (I) in the
aqueous solution ranges from 500 to 8000 ppm.
8. The process according to claim 7, characterized in that the
concentration of the polymer having general formula (I) in the
aqueous solution ranges from 1500 to 5000 ppm.
9. The process according to claim 1, characterized in that in the
polymer having general formula (I) n=0.95, m=0.05, x=3,
X.sub.1.dbd.H, X.sub.2.dbd.CH.sub.3, R.sub.1CH.sub.3,
R.sub.2.dbd.CH.sub.3, R.sub.3=CH.sub.3.
10. The process according to claim 1, characterized in that in the
polymer having general formula (I) n=0.90, m=0.1, x=3, X.sub.1H,
X.sub.2.dbd.CH.sub.3, R.sub.1.dbd.CH.sub.3, R.sub.2.dbd.CH.sub.3,
R.sub.3.dbd.CH.sub.3.
11. The process according to claim 1, characterized in that it is
preceded by an optional pretreatment step (preflush).
12. The process according to claim 11, characterized in that the
pretreatment step is effected with an aqueous solution containing a
surface-active agent.
13. The process according to claim 1, characterized in that at the
end of the above process, an optional over-flush step is effected,
or a treatment of the formation itself with brine or gas or oil.
Description
[0001] The present invention relates to a process for reducing the
production of water in oil wells which comprises the injection of
an aqueous solution of a cationic polymer into the formation.
[0002] The coproduction of water is a fact which concerns, to
varying extents and with different times, all oil or gas wells, and
which can have strong negative economic repercussions. The
excessive production of water in fact causes both an increase in
the costs relating to the disposal of the water and also to a
reduction in income due to the limited productivity of
hydrocarbons.
[0003] In gas fields, moreover, a high water-cut (i.e. the ratio
between the water flow-rate of a well and the total
water+hydrocarbon flow-rate) can lead to the flooding of the well
and consequently its closure.
[0004] Furthermore, in the future, problems associated with the
production of water will become even more important in view of the
characteristics of fields currently in production and of new
exploration frontiers. The production of existing fields in fact
(increasingly more mature) is normally characterized by a water-cut
which increases with time. The exploration frontiers moreover are
moving towards offshore reservoirs, often in deep water, and in
areas often characterized by severe environmental regulations
[0005] In wells with a high water-cut, the problem can generally be
solved by the mechanical insulation of the production area or by
recompletion or workover. The latter solution however is extremely
onerous and can cause the loss of enormous volumes of hydrocarbons
present in the micro-levels still not influenced by the arrival of
water.
[0006] "Water shut-off" interventions with gelifying chemical
systems (usually polyacrylamides cross-linked with Cr(III) or with
systems based on silicates), can represent a valid alternative to
mechanical insulation; these compositions, injected into the
formation, completely block the movement of the fluids in the zones
treated. With this technique, it is possible to totally reduce or
eliminate the production of water at accessible costs. This
technology however only has a high probability of success when it
is possible to identify and selectively insulate the water
production areas during the treatment, so as not to damage
production from the layers still saturated with hydrocarbons.
[0007] Finally, the RPM (Relative Permeability Modifier) technology
is based on the injection, in all intervals open for production, of
a chemical agent capable of selectively reducing the permeability
to water. The chemical systems used in this type of treatment are
hydrosoluble polymers which modify the permeability of the
formation following adsorption on the rock surface. In this way,
the permeability in the high water-cut intervals is selectively
reduced, whereas the permeability of the intervals which produce
hydrocarbons remains unaltered. Intervening with this approach,
when appropriate, has numerous advantages with respect to the
conventional technologies, in particular: (i) limit risk of damage,
(ii) low environmental impact, (iii) low cost of the treatment
thanks to interventions of the "bullheading" type.
[0008] The condition necessary for effective treatment with a
permeability modifier polymer is that the polymer itself must
interact with the rock surface creating a layer capable of
modifying the flow properties of the porous medium. The polymer
must therefore have a particularly strong attractive interaction
with the rock surface, in order to maximize the adsorption and
stability of the layer of adsorbed polymer, over a period of
time.
[0009] The polymers used so far have various limitations which have
delayed the diffusion of the RPM technology. In particular:
polyacrylamides (PAM) have a poor efficacy and reduced duration of
the treatment due to the limited thermal stability; polyactylamides
modified by the introduction of cationic groups have a good
efficacy but low resistance to temperature; biopolymers (such as
scleroglucan) have infectivity problems as a result of the high
viscosity of the polymeric solution and its tendency to
flocculate.
[0010] Experts in the field have consequently felt the necessity of
finding polymers capable of being more effectively adsorbed on rock
matrixes and therefore capable of selectively reducing the
permeability to water and also resistant to the temperature of the
formation.
[0011] It has now been found that particular cationic polymers
adequately satisfy the above demands, and are particularly
thermally stable at medium-high temperatures. Adsorption tests
carried out on siliceous sand using polymers containing cationic
groups and analogous non-ionic polymers have in fact demonstrated
that the former are more strongly adsorbed on the rock with respect
to the latter, as a result of the attractive interaction between
the surface of the negatively charged sand and the positively
charged polymer.
[0012] In accordance with this, the present invention relates to a
process for reducing the production of water in oil wells which
comprises the injection into the formation around the well of an
aqueous solution of one or more polymers selected from those having
general formula (I): ##STR1## wherein [0013] n ranges from 0.70 to
0.98, preferably from 0.80 to 0.95; [0014] m ranges from 0.30 to
0.02, preferably from 0.20 to 0.05; [0015] n+m=1; [0016] X.sub.1
and X.sub.2, the same or different, are selected from H and
CH.sub.3; [0017] R.sub.1, R.sub.2, R.sub.3, the same or different,
are selected from C.sub.1-C.sub.10 monofunctional hydrocarbyl
groups; preferably C.sub.1-C.sub.3 alkyl radicals; [0018] x ranges
from 2 to 5, preferably x=3.
[0019] In the preferred embodiment, in the compound having general
formula (I) the polymers have: (1): n=0.95, m=0.05, x=3,
X.sub.1.dbd.H, X.sub.2.dbd.CH.sub.3, R.sub.1.dbd.CH.sub.3,
R.sub.2.dbd.CH.sub.3, R.sub.3.dbd.CH.sub.3; or (2): n=0.90, m=0.1,
x=3, X.sub.1.dbd.H, X.sub.2.dbd.CH.sub.3, R.sub.1.dbd.CH.sub.3,
R.sub.2.dbd.CH.sub.3, R.sub.3.dbd.CH.sub.3. The molecular weight of
the polymers usually ranges from 1.5 to 12 million.
[0020] The aqueous solution which can be used in the process of the
present invention contains a quantity of polymer of the compound
having general formula (I) preferably ranging from 500 to 8000 ppm,
even more preferably from 1500 to 5000 ppm.
[0021] Any type of water available provided it has no suspended
solids, can be used as carrying medium, as the compound having
general formula (I) is neither influenced by the type or quantity
of anions and cations usually contained in water.
[0022] The aqueous solution of the present invention normally has a
viscosity ranging from 1.5 to 10 cP, much lower values than those
of the gelifying solutions.
[0023] The volume of aqueous solution to be injected into the
formation depends on the height of the production formation to be
treated and on the depth to which the solution must penetrate
(invasion radius).
[0024] The flow-rate of the aqueous solution to be injected is
selected in relation to the type of formation to be treated.
Furthermore the aqueous solution to be injected can be fed into the
formation at the desired pressure, provided this is not higher than
the fracture pressure. It is known to experts in the field that it
is advantageous for the solution to be injected as rapidly as
possible, compatibly with the characteristics of the formation, in
order to reduce the treatment time and consequently
production-stoppage, to the minimum.
[0025] When considered necessary, the process of the present
invention can be preceded by an optional pretreatment step
(preflush) which can be carried out for example with an aqueous
solution containing a surface-active agent, in order to clean the
formation to be treated and obtain a more effective adsorption of
the polymer.
[0026] In the preferred embodiment, the process of the present
invention is preferably followed by an overflush step, i.e.
treatment of the formation with brine or gas or oil, in order to
push the polymer into the formation. The overflush with gas also
has the purpose of re-establishing the connectivity of the gas
layer (in gas wells).
[0027] Finally, at the end of the injection of the aqueous solution
of the compound having general formula (I), a shut-in step is
preferably effected, i.e. closure of the well to allow a more
effective adsorption of the polymer on the rock matrix.
[0028] The process of the present invention has many advantageous
aspects, and in particular requires limited quantities of polymer
having general formula (I). Furthermore it has the unexpected
advantage of being applicable to both gas and oil formations, with
temperatures up to about 70.degree. C.
[0029] The following examples are provided for a better
understanding of the present invention.
EXAMPLES
[0030] The polymer (called FO, produced by Floerger) used in the
examples has the following formula. It is a
poly{acrylamide-methacrylamide (propyltrimethylammonium)}
copolymer. The polymer has a molecular weight equal to 5
million.
[0031] For comparative purposes, in the experimental part another
cationic polymer is also used, which is not a part of the
invention. This is a cationic polymer (MCAT, produced by MI
Drilling Fluids), a
poly{acrylamide-acrylamide-(methyltrimethylammonium)} copolymer.
The polymer has a molecular weight equal to 2 million.
[0032] Both products are in the form of a white powder. In
particular, the product FO has a particle-size ranging from 10-100
mesh. ##STR2##
Chemical Structure of the Cationic Polymer FO
[0033] (FO3150: n=0.95, m=0.05; FO3190: n=0.90, m=0.1) ##STR3##
Chemical Structure of the Cationic Polymer MCAT
(p=0.95, q=0.05)
Example 1
Performances of the Cationic Polymers FO and MCAT
[0034] The performances of the polymers FO and MCAT were evaluated
by means of: a) Adsorption test on sand of the solutions; b)
Thermal stability evaluation by means of NMR analysis; c) Core
test
1a--Static Adsorption Test at a Temperature of 25.degree. C.
[0035] The polymer solutions were prepared in brine (filtered and
degassed solution of KCl 2%) at concentrations of 1000 or 2000 ppm.
After putting a certain quantity of sand (3-5 g) in contact with
the polymeric solution in a hermetically sealed glass container,
the solution with the sand is put under stirring at the desired
temperature to favour contact between the polymer and surface of
the sand. After about 24 hours at 25.degree. C., the quantity of
polymer adsorbed at the interface is determined by difference
(between that initially charged and that remaining in the solution
after the test) by means of TOC analysis (Total Organic
Carbon).
[0036] The tests were carried out using sand with a prevalently
siliceous and clay composition. Table 1 shows a comparison between
the adsorption values of the FO polymers and of the comparative
MCAT polymer. TABLE-US-00001 TABLE 1 Adsorption comparison, at
25.degree. C., of solutions of the FO polymer (3150) on sand
(quartzite and reservoir) and analogous solutions of the MCAT
polymer. The reservoir sand used has the following composition:
reservoir sand 1: quartz 50%, K-feldspar 6%, plagioclase 15%,
calcite 6%, dolomite 1%, clays/micas 22% reservoir sand 2: quartz
49%, plagioclase 17%, calcite 21%, clays/micas 4% Conc. Adsorption
Adsorption Temp. solution (mg/g sand) (mg/g sand) (.degree. C.)
(ppm) FO3150 MCAT Quartzite 25 1000 0.24 0.13 25 2000 0.3 0.32
Reservoir 1 25 1000 0.75 0.7 25 2000 1.6 1.15 Reservoir 2 25 1000
-- 0.78 2000 1.09
[0037] It can be observed that all the polymers have a high
adsorption (both on quartzite sand and on reservoir sand), a
necessary but insufficient condition for the success of the RPM
treatment.
[0038] For successful treatment, in fact, the thermal stability of
the polymer must also be considered, in particular of the active
cationic group, at the desired temperature.
1b1--Evaluation of the Thermal Stability by Means of NMR
Analysis
[0039] The thermal stability of the product was evaluated by means
of NMR analysis carried out on aqueous solutions of the polymers FO
3150 and MCAT, and in particular the concentration of active
cationic groups present at the different temperatures was
determined.
[0040] Table 2 provides a comparison between the thermal stability
of the polymer MCAT (in terms of percentage of cationic groups
hydrolyzed at the test temperature) and the polymer FO of the
present invention. TABLE-US-00002 TABLE 2 Comparison between the
thermal stability of the solution of the polymer MCAT and of the
solution of the polymer FO 3150 of the present invention after 21
days (via NMR analysis) MCAT FO % of cationic % of cationic
Temperature groups hydrolyzed groups hydrolyzed 48.degree. C. 58
n.d. 70.degree. C. >99 5
[0041] A significant degradation of the active cationic groups of
the polymer MCAT can be observed at 70.degree. C. The presence of a
single --(CH.sub.2)-- group attached to the acrylamide group
probably makes the bond particularly labile at high
temperatures.
[0042] The polymer FO of the present invention, on the contrary, is
thermally stable.
1b2--Static Adsorption Test at Temperatures of 70.degree. C.
[0043] Following the procedure described in 1a, adsorption tests
were effected on sand at a temperature of 70.degree. C., using the
polymer MCAT and the polymer FO of the present invention.
[0044] The results of the test are indicated in Table 3.
TABLE-US-00003 TABLE 3 Comparison of the adsorption of solutions of
the polymer FO 3150 on sand (quartzite and reservoir) and analogous
solutions of the polymer MCAT. The reservoir sand used has the
mineralogical composition indicated in the description of Table 1.
Conc. Adsorption Adsorption Temp. solution (mg/g sand) (mg/g sand)
(.degree. C.) (ppm) FO3150 MCAT Quartzite 70 1000 0.25 0.035 70
2000 0.22 0.15 Reservoir 1 70 1000 0.7 0.4 70 2000 1.5 0.8
[0045] It can be observed that the polymer FO has high adsorptions
both on clean sand (quartzite) and reservoir sand. Furthermore the
adsorptions are comparable both at room temperature and at
70.degree. C. (see Table 1 as a comparison), indicating the fact
that the polymer has not undergone substantial structural
modifications, i.e. that the active cationic groups are stable at
70.degree. C. The polymer MCAT, on the contrary, shows a reduced
adsorption with respect to the value observed at room temperature,
in accordance with the degradation of the active cationic
groups.
1-c--Test in a Porous Medium
[0046] After verifying the adsorption of the polymer on rock, the
efficacy of the polymer MCAT was evaluated in selectively reducing
permeability to water by means of a test in a porous medium. Two
tests were effected in a porous medium at two different
temperatures: 48 and 70.degree. C.
[0047] The sandpack was prepared using about 40 grams of sand, so
as to obtain a core length equal to about 5 cm to which 2 cm of
gravel having 20-40 mesh, are added, one at the head and one at the
tail, held by two 70-mesh metallic nets. The diameter of the
sandpack is equal to 1''.
[0048] Once the sandpack has been assembled in the Hassler steel
cell, a boundary pressure of 20 bars is established to avoid the
bypassing of the fluids between the VITON tube (which contains the
core) and the porous medium. The following procedure is adopted:
[0049] Saturation under vacuum of the sandpack with brine (2% KCl)
and subsequent determination of the porosity and absolute
permeability at room temperature and at the temperature of
interest. [0050] Flush of the brine with gas (nitrogen previously
humidified) or oil (crude field oil): determination of the initial
permeability relating to the gas (K.sub.in gas) or crude field gas
(Kin crude field oil) and the corresponding saturation in water.
[0051] Flush of the gas (or crude field oil) with brine:
[0052] determination of the initial permeability relating to the
brine (K.sub.in brine) and the corresponding saturation in gas (or
crude field oil). [0053] Injection of the polymeric solution of
MCAT (1500 ppm) previously filtered and degassed (from 10 to 12
pore volumes) at a constant flow-rate. During the flush the
pressure values are collected together with the outgoing fractions
to determine the quantity of polymer adsorbed. [0054] Shut-in of 24
hours. [0055] Flush of the polymer with brine (2% KCl) at a
constant flow-rate (about 1 PV/h). During the flushing the pressure
vales are recorded and the outgoing fractions collected. [0056]
Determination of the permeability to brine after the treatment with
the polymer (K.sub.finbrine). [0057] Determination of the
permeability to gas or oil (crude field oil) after the treatment
with the polymer (K.sub.fin gas, K.sub.fin crude field oil) and of
the saturation in brine.
[0058] The results of the tests are summarized in Table 4.
TABLE-US-00004 TABLE 4 Results of the test in a porous medium with
the polymer MCAT (1500 ppm). The reduction in permeability to water
was calculated after injecting from 600 to 900 pore volumes (PV) of
brine. The reservoir sand used has the composition indicated in the
description of Table 1. K initial Reduction Reduction Temp. brine
brine gas Sand (.degree. C.) (mD) permeability (%) permeability (%)
Reservoir 2 48 78 77 20 Reservoir 2 70 122 22 --
[0059] It can be observed that the polymer MCAT is effective as
permeability modifier relating to a temperature of about 50.degree.
C. At 70.degree. C. the reduction in permeability to brine is
significantly reduced with respect to what is observed at lower
temperatures (22% against 77%). This is in accordance with the data
of the static. adsorption tests and with the NMR analyses carried
out on the solutions, which showed a considerable degradation of
the polymer MCAT at 70.degree. C. with an almost complete
detachment of the active cationic groups. The cationic group is
essential for obtaining a good adsorption and consequently a good
reduction in the permeability to brine.
Example 2
Performances of the Polymer FO of the Present Invention
[0060] Once the thermal stability of the polymer FO, whose
solutions proved to be stable at temperatures equal to 70.degree.
C., has been defined, the performances of the product were
evaluated by means of adsorption tests on sand and tests in a
porous medium,-in which the reduction in permeability to brine and
the effect on permeability to hydrocarbons (gas, oil), were
evaluated.
2-a--Static Adsorption Test
[0061] The adsorption tests on sand were carried out using two
different formulations of the polymer, in particular: [0062] FO3150
(5% moles MAPTAC, 95% moles AM; n=0.95, m=0.05) [0063] FO3190 (10%
moles MAPTAC, 90% moles AM; n=0.90, m=0.1) wherein MAPTAC:
methacrylamide propyl trimethylammonium, AM: acrylamide.
[0064] Table 5 shows a comparison of adsorption data of the two FO
polymers which differ in the content of the cationic component: 5%
in moles in FO3150, 10% in moles in FO3190. TABLE-US-00005 TABLE 5
Comparison of the adsorption of solutions of the polymer FO3150 (5%
cationicity) and FO3190 (10% cationicity) on sand (quartzite and
reservoir sand). The reservoir sand used has the composition
indicated in the description of Table 1. FO 3150 FO 3190 Conc.
Conc. solution Adsorption Temp. solution Adsorption Sand Temp.
(.degree. C.) (ppm) (mg/g sand) (.degree. C.) (ppm) (mg/g sand)
Reservoir 1 25 1000 0.75 25 1000 0.89 25 2000 1.6 25 2000 1.77 70
1000 0.7 70 1000 0.65 70 2000 1.5 70 2000 1.6
[0065] It can be observed that, within this composition range, the
degree of cationicity does not seem to influence the adsorption
level: the quantity of polymer adsorbed is about the same for both
the polymer FO3150 and the polymer FO3190.
2-b--Tests in a Porous Medium.
[0066] In the tests in a porous medium, carried out with the
purpose of evaluating the efficacy of the FO polymer in reducing
permeability to brine, the procedure described in Example 1-c was
adopted. Also in this case, a polymeric solution (in brine KCl 2%)
of 1500 ppm, was used.
The following tests were carried out:
[0067] test in a porous medium on sandpack (quartzite) at room
temperature: determination of the reduction in the absolute
permeability to brine [0068] test in a porous medium on sandpack
(reservoir sand 1) at 70.degree. C.: determination of the reduction
in permeability relating to brine and evaluation of the effect on
the permeability relating to gas. The reservoir sand used has the
mineralogical composition indicated in the description of Table 1.
[0069] test in a porous medium on core (clashach) at 70.degree. C.:
determination of the reduction in permeability relating to brine
and evaluation of the effect on the permeability relating to oil.
The core (length 10 cm, diameter 2.54 cm, pore volume 9.28
cm.sup.3) has the following mineralogical composition: quartz 95%,
K-feldspar 5%.
[0070] In the tests in the porous medium carried out with the
brine-oil biphasic system, a crude field oil was used.
[0071] The results of the test are indicated in Table 6.
TABLE-US-00006 TABLE 6 Tests in a porous medium effected with the
FO polymer. Gas was used for the test carried out with reservoir
sand; a typical crude field oil was used for the test with
Clashach. Initial Temper- Reduction Reduction Reduction permeabil.
ature permeabil. permeabil. permeabil. Core (mD) (.degree. C.)
brine (%) gas (%) oil (%) Quartzite 1182 Room 59.4 -- -- temp.
Reservoir 26 70 94 31 -- 1 Clashach 47 70 62 -- 18
* * * * *